An internal combustion engine is used as a motor vehicle drive unit. The expression internal combustion engine encompasses diesel engines and also Otto-cycle engines and hybrid internal combustion engines, that is to say internal combustion engines which are operated using a hybrid combustion process.
In the development of internal combustion engines, it is a basic aim to minimize fuel consumption, wherein the emphasis in the efforts being made is on obtaining an improved overall efficiency. Fuel consumption and thus efficiency pose a problem in particular in the case of Otto-cycle engines that is to say in the case of an applied-ignition internal combustion engine. The reason for this lies in the principle of the operating process of the Otto-cycle engine. Load control is generally carried out by means of a throttle flap provided in the intake system. By adjusting the throttle flap, the pressure of the inducted air downstream of the throttle flap can be reduced to a greater or lesser extent. The further the throttle flap is closed, that is to say the more said throttle flap blocks the intake system, the higher the pressure loss of the inducted air across the throttle flap, and the lower the pressure of the inducted air downstream of the throttle flap and upstream of the inlet into the at least two cylinders, that is to say combustion chambers. In this way, for a constant combustion chamber volume, it is possible for the air mass, that is to say the quantity, to be set by means of the pressure of the inducted air. This also explains why quantity regulation has proven to be disadvantageous specifically in part-load operation, because low loads require a high degree of throttling and a pressure reduction in the intake system, as a result of which the charge exchange losses increase with decreasing load and increasing throttling.
To reduce the described losses, various strategies for dethrottling an applied-ignition internal combustion engine have been developed. One example approach for dethrottling the Otto-cycle engine is by operating the engine with direct injection. The direct injection of the fuel is a suitable means for realizing a stratified combustion chamber charge. The direct injection of the fuel into the combustion chamber thus permits quality regulation in the Otto-cycle engine, within certain limits. The mixture formation takes place by the direct injection of the fuel into the cylinders or into the air situated in the cylinders, and not by external mixture formation, in which the fuel is introduced into the inducted air in the intake system.
Another example of optimizing the combustion process of an Otto-cycle engine consists in the use of an at least partially variable valve drive. By contrast to conventional valve drives, in which both the lift of the valves and the timing are invariable, these parameters which have an influence on the combustion process, and thus on fuel consumption, can be varied to a greater or lesser extent by means of variable valve drives. If the closing time of the inlet valve and the inlet valve lift can be varied, this alone makes throttling-free and thus loss-free load control possible. The mixture mass which flows into the combustion chamber during the intake process is then controlled not by means of a throttle flap but rather by means of the inlet valve lift and the opening duration of the inlet valve. Variable valve drives are however very expensive and are therefore often unsuitable for series production.
Yet another example approach includes partial cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. The efficiency of the Otto-cycle engine in part-load operation can be improved, that is to say increased, by means of a partial deactivation because the deactivation of one cylinder of a multi-cylinder internal combustion engine increases the load on the other cylinders, which remain in operation. During partial cylinder deactivation, if the engine power remains constant, the throttle flap may have to be opened further in order to introduce a greater air mass into operational cylinders, whereby dethrottling of the internal combustion engine may be attained. During the partial deactivation, the cylinders which are permanently in operation operate in the region of higher loads, at which the specific fuel consumption is lower. The load collective is shifted toward higher loads.
The cylinders which remain in operation during the partial deactivation furthermore exhibit improved mixture formation owing to the greater air mass or mixture mass supplied. Further advantages with regard to efficiency are attained in that a deactivated cylinder, owing to the absence of combustion, does not generate any wall heat losses owing to heat transfer from the combustion gases to the combustion chamber walls.
Even though diesel engines (auto-ignition internal combustion engines), owing to the quality regulation on which they are based, exhibit greater efficiency, that is to say lower fuel consumption, than Otto-cycle engines in which the load is adjusted by means of throttling or quantity regulation with regard to the charge of the cylinders there is potential for improvement and a demand for improvement with regard to fuel consumption and efficiency.
One concept for reducing fuel consumption, also in the case of diesel engines, is cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. The efficiency of the diesel engine in part-load operation can be improved, by means of a partial deactivation, because, even in the case of the diesel engine, in the case of constant engine power the deactivation of at least one cylinder of a multi-cylinder internal combustion engine increases the load on the other cylinders still in operation, such that said cylinders operate in regions of higher loads, in which the specific fuel consumption is lower. The load collective in part-load operation of the diesel engine is shifted toward higher loads. With regard to the wall heat losses, the same advantages are attained as discussed above in relation to Otto-cycle engine.
In the case of diesel engines, the partial deactivation is also intended to prevent the fuel-air mixture from becoming too lean as part of the quality regulation in the event of decreasing load as a result of a reduction of the fuel quantity used. The multi-cylinder internal combustion engines with partial deactivation, and the associated methods for operating said internal combustion engines as used currently have considerable potential for improvement, as will be explained briefly below on the basis of a diesel engine as an example.
In a direct-injection diesel engine, if, for the purpose of the partial deactivation, the fuel supply to the deactivatable cylinders is stopped, that is to say discontinued, the deactivated cylinders continue to participate in the charge exchange if the associated valve drive of said cylinders is not deactivated or cannot be deactivated. The charge exchange losses thus generated lessen, and counteract, the improvements achieved with regard to fuel consumption and efficiency by means of the partial deactivation, such that the benefit of the partial deactivation is at least partially lost, that is to say the partial deactivation in fact yields an altogether less pronounced improvement.
In practice, it is often not expedient for the above-described disadvantageous effects to be remedied through the provision of switchable valve drives on the inlet side and on the outlet side, because switchable valve drives are very expensive and are generally not suitable for series production.
Furthermore, in the case of internal combustion engines supercharged by means of exhaust-gas turbocharging, switchable valve drives can lead to further problems because the turbine of an exhaust-gas turbocharger has to be configured for a certain exhaust-gas flow rate, and thus also for a certain number of cylinders. If the valve drive of a deactivated cylinder is deactivated, the overall mass flow through the cylinders of the internal combustion engine is reduced owing to the omission of the mass flow through the deactivated cylinders. The exhaust-gas mass flow conducted through the turbine decreases, and the turbine pressure ratio commonly also decreases as a result. This would have the effect that the charge pressure ratio likewise decreases, that is to say the charge pressure falls, and only a small amount of fresh air or charge air is or can be supplied to the cylinders that remain operational. The small charge-air flow may also cause the compressor to operate beyond the surge limit. In the context of the present disclosure, the expression charge air is used even if the internal combustion engine is not supercharged but is a naturally aspirated engine.
The effects described above lead to a restriction of the practicability of the partial deactivation, specifically to a restriction of the load range in which the partial deactivation can be used. A reduced charge-air flow rate that is supplied to the cylinders which are operational during the partial deactivation reduces the effectiveness or the quality of the combustion and has an adverse effect on the fuel consumption and pollutant emissions.
The charge pressure during a partial deactivation, and thus the charge-air flow rate supplied to the cylinders that remain operational, could for example be increased by means of a small configuration of the turbine cross section and by means of simultaneous exhaust-gas blow-off, whereby the load range relevant for a partial deactivation would also be expanded again. This approach however has the disadvantage that the supercharging behavior is inadequate when all the cylinders are operational.
The charge pressure during a partial deactivation, and thus the charge-air flow rate supplied to the cylinders that are still operational, could also be increased by virtue of the turbine being equipped with a variable turbine geometry, which permits an adaptation of the effective turbine cross section to the present exhaust-gas mass flow. The exhaust-gas back pressure in the exhaust-gas discharge system upstream of the turbine would then however simultaneously increase, leading in turn to higher charge-exchange losses in the cylinders that are still operational.
To counteract the above-described problems with regard to the low charge-air flow rate supplied to the cylinders that remain operational during the partial deactivation, a throttle element may be provided in the at least one intake line of each load-dependently switchable cylinder. By means of the throttle element, the size of the flow cross section of the intake line can be varied, whereby the charge-air flow rate supplied to the deactivated cylinder during partial deactivation of the internal combustion engine can be adjusted. In this way, it is possible for the supply of charge air to the deactivated cylinders, that is to say the charge-air flow rate supplied during partial deactivation, to be reduced and controlled, possibly even eliminated entirely, without the switchable cylinders having to be equipped with switchable valve drives, which entail high costs. In one embodiment, the cylinders which are operational during the partial deactivation may also be fitted with intake throttle elements instead of a variably actuated valve.
Through actuation of the throttle element provided in the intake line of a deactivated cylinder, the flow cross section of the intake line is varied, in particular reduced in size, whereby the charge-air flow rate supplied to the deactivated cylinder during the partial deactivation can be adjusted, metered and controlled.
As has already been described, the deactivated cylinders may continue to participate in the charge exchange because the associated non-switchable valve drive of said cylinders continues to be actuated, that is to say continues to operate, and is not deactivated together with the cylinders. The supply of charge air may however be reduced, as described above, by means of a throttle element. Less charge air or no charge air is supplied, in order that the charge exchange losses of the deactivated cylinders are reduced.
The reduced charge-air flow through the at least one deactivated cylinder leads (in relation to an unchanged charge-air flow with the intake line fully open) to reduced heat transfer owing to convection, such that the deactivated cylinders do not cool down, or cool down to a lesser extent, during the partial deactivation. This has advantages with regard to pollutant emissions, in particular with regard to the emissions of unburned hydrocarbons, because the deactivated cylinders reach or exhibit their operating temperature again immediately after the end of the partial deactivation.
The reduction of the charge-air flow by means of a throttle element has further advantages in relation to internal combustion engines in which the charge-air supply is prevented entirely by means of switchable valve drives, said further advantages resulting substantially from the fact that the mass flow through the internal combustion engine is greater in the case of a reduction of the charge-air supply than in the case of the supply of charge air being prevented entirely.
Advantages are obtained in the case of exhaust gas-turbocharged internal combustion engines. The greater mass flow leads to a higher turbine pressure ratio and thus to a higher charge pressure, such that a greater charge-air flow rate can be provided to the cylinders that are operational during partial deactivation. This also expands the range of applicability of the partial deactivation, specifically the load range in which partial deactivation can be used, and improves the quality of the combustion and thus the consumption and emissions characteristics of the internal combustion engine.
The inventors herein have identified the above issues and identified an approach by which the issues described above may be at least partly addressed. The disclosure relates to an internal combustion engine having at least two cylinders, in which each cylinder has at least one outlet opening which is adjoined by an exhaust line for discharging the exhaust gases via an exhaust-gas discharge system. Each cylinder has at least one inlet opening which is adjoined by an intake line for the supply of charge air via an intake system. At least two cylinders are configured in such a way that they form at least two groups wherein each group comprises of at least one cylinder. At least one cylinder of a first group is a cylinder which is operational even in the event of a partial deactivation of the internal combustion engine, and the at least one cylinder of a second group is formed as a load-dependently switchable cylinder. An inlet-side throttle element may be provided in the at least one intake line of the at least one load-dependently switchable cylinder. By means of the throttle element, the size of the flow cross section of the intake line can be varied, whereby the charge-air flow rate supplied to the at least one deactivated cylinder in the event of a partial deactivation of the internal combustion engine can be adjusted. Each outlet opening of a load-dependently switchable cylinder may be equipped with an at least partially variable valve drive, with an outlet valve which opens up or shuts off the outlet opening, an oscillating outlet valve realizing a valve lift Δh between an open position and a closed position and opening up the associated outlet opening during an opening duration Δt.
In the case of the internal combustion engine according to the disclosure, in addition to the at least one inlet-side throttle element, which is provided in the intake system of the at least one load-dependently switchable cylinder, each outlet opening of a load-dependently switchable cylinder is equipped with an at least partially variable valve drive.
While the inlet-side throttle element controls the supply of charge air to a deactivated cylinder, that is to say reduces or possibly even eliminates the charge-air flow rate supplied during partial deactivation, an outlet valve actuated by means of an at least partially variable valve drive serves to prevent or reduce an undesired backflow of exhaust gas into a deactivated cylinder of the second group. Furthermore, the charge exchange losses of a deactivated cylinder can be reduced through suitable control of the outlet valve. The opening of an outlet valve should preferably be prevented when, in the associated deactivated cylinder, negative pressure prevails or a pressure prevails which is lower than that in the exhaust-gas discharge system.
An outlet valve is intended to control the discharge of the exhaust gas out of a cylinder, which is deactivated during partial deactivation of the internal combustion engine, of the second group. During partial deactivation, it is not hot exhaust gas but rather charge air or fresh air that is discharged. However, at least during the first working cycle of the partial deactivation, the exhaust gas of the preceding working cycle, and thus the hot exhaust gas of the most recent fired working cycle, is discharged via the exhaust-gas discharge system. Then, during the following working cycles of the partial deactivation, charge air or fresh air is discharged. Nevertheless, the discharge of hot exhaust gas will be referred to in the context of the present disclosure.
During partial cylinder deactivation, the outlet valve of the second group (switchable) of cylinders may be regulated to control the engine temperature. In one example, if during engine operation with partial cylinder deactivation, there is a drop in engine temperature, the outlet valve may be opened to a degree to allow warm exhaust to enter the cylinders thereby increasing engine temperature. In another example, the intake throttle element(s) and the outlet valve(s) may be regulated to prevent surge.
The internal combustion engine according to the disclosure has at least two cylinders or at least two groups with in each case at least one cylinder. In this respect, internal combustion engines with three cylinders which are configured in three groups with in each case one cylinder, or internal combustion engines with six cylinders which are configured in three groups with in each case two cylinders, are likewise internal combustion engines according to the disclosure. Within the context of a partial deactivation, the three cylinder groups may be activated or deactivated in succession, whereby two-time switching may also be realized. The partial deactivation is thereby further optimized. The cylinder groups may also comprise a different number of cylinders.
The embodiment of the internal combustion engine optimizes the efficiency of the internal combustion engine in part-load operation, that is to say at low loads, wherein a low load Tlow is preferably a load which amounts to less than 50%, preferably less than 30%, of the maximum load Tmax,n at the present engine speed n.
In one example, at least one inlet-side throttle element in the internal combustion engine, is a valve. In another example, the inlet-side throttle element may be a pivotable flap. In yet another example, inlet-side throttle element may be continuously adjustable. The configuration of the throttle element as a continuously adjustable throttle element permits precise dosing of the charge-air flow rate introduced into the deactivated cylinders. The metering of the charge-air flow rate may be performed in an operating point-specific manner, in particular with regard to the lowest possible charge exchange losses and/or a required charge pressure. The control of the throttle element may take into consideration the load T, the engine speed n, the coolant temperature in the case of a liquid-cooled internal combustion engine, the oil temperature and other engine operating parameters. In a further example, the throttle element may be switchable in two-stage or multi-stage fashion. The throttle element may be electrically, hydraulically, pneumatically, mechanically or magnetically controllable, by means of an engine controller.
Embodiments of the internal combustion engine are advantageous in which a supercharging arrangement is provided. In this case, embodiments of the internal combustion engine are advantageous in which at least one exhaust-gas turbocharger is provided which comprises a turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system.
The advantage of the exhaust-gas turbocharger for example in relation to a mechanical charger is that no mechanical connection for transmitting power is required between the charger and internal combustion engine. While a mechanical charger extracts the energy required for driving it entirely from the internal combustion engine, and thereby reduces the output power and consequently adversely affects the efficiency, the exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases.
Supercharged internal combustion engines are preferably equipped with a charge-air cooling arrangement by means of which the compressed combustion air is cooled before it enters the cylinders. In this way, the density of the supplied charge air is increased further. In this way, the cooling likewise contributes to a compression and improved charging of the combustion chambers, that is to say to an improved volumetric efficiency. It may be advantageous for the charge-air cooler to be equipped with a bypass line in order to be able to bypass the charge-air cooler if required, for example after a cold start.
Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and an improved power-to-weight ratio. If the swept volume is reduced, it is thus possible, given the same vehicle boundary conditions, to shift the load collective toward higher loads, at which the specific fuel consumption is lower.
Problems are encountered in the configuration of the exhaust-gas turbocharging, wherein it is basically sought to obtain a noticeable performance increase in all engine speed ranges. A severe torque drop is commonly observed in the event of a certain engine speed being undershot. The torque characteristic of a supercharged internal combustion engine can be improved through various measures, for example by virtue of a plurality of superchargers—exhaust-gas turbochargers and/or mechanical superchargers being provided in a parallel and/or series arrangement in the exhaust-gas discharge system.
At least one exhaust-gas aftertreatment system, for example an oxidation catalytic converter, a three-way catalytic converter, a storage catalytic converter, a selective catalytic converter and/or a particle filter, may be provided in the exhaust-gas discharge system.
In the case of internal combustion engines having four cylinders in an in-line arrangement, the two outer cylinders and the two inner cylinders may form in each case one group.
At least one exhaust-gas recirculation (EGR) arrangement may be provided to the internal combustion engine. EGR comprises a recirculation line which branches off from the exhaust-gas discharge system and issues into the intake system. EGR is a suitable means for reducing the nitrogen oxide emissions. EGR rate xEGR may be determined as xEGR=mEGR/(mEGR+mfresh air), where mEGR denotes the mass of recirculated exhaust gas and mfresh air denotes the supplied fresh air which, if appropriate, is conducted through a compressor and compressed. To obtain a considerable reduction in nitrogen oxide emissions, high exhaust-gas recirculation rates are required which may be of the order of magnitude of xEGR≈60% to 70%. A valve may arranged in the recirculation line of the EGR arrangement for adjusting the EGR flow rate.
In the case of internal combustion engines having at least one exhaust-gas turbocharger and an exhaust-gas recirculation arrangement, embodiments are advantageous in which the recirculation line of the exhaust-gas recirculation arrangement branches off from the exhaust-gas discharge system upstream of the turbine of the at least one exhaust-gas turbocharger and issues into the intake system downstream of the compressor. In the case of said so-called high-pressure EGR arrangement, the exhaust gas is extracted from the exhaust-gas discharge system upstream of the turbine and is fed into the intake system downstream of the compressor, whereby the exhaust gas need not be subjected to exhaust-gas aftertreatment, in particular supplied to a particle filter, before being recirculated, because there is no risk of fouling of the compressor.
In the case of the operation of an internal combustion engine with exhaust-gas turbocharging and the simultaneous use of high-pressure EGR, a conflict may however arise because the recirculated exhaust gas is no longer available for driving the turbine. In the event of an increase in the exhaust-gas recirculation rate, the exhaust-gas flow introduced into the turbine decreases. The reduced exhaust-gas mass flow through the turbine leads to a lower turbine pressure ratio, as a result of which the charge-pressure ratio also falls, which equates to a smaller charge-air flow.
In order to overcome the above mentioned issue, low-pressure EGR may be used. By contrast to high-pressure EGR, in the case of low-pressure EGR, exhaust gas which has already flowed through the turbine is introduced into the intake system. For this purpose, the low-pressure EGR arrangement has a recirculation line which branches off from the exhaust-gas discharge system downstream of the turbine and issues into the intake system preferably upstream of the compressor. The exhaust gas which is recirculated via the low-pressure EGR arrangement to the inlet side is mixed with fresh air. The mixture of fresh air and recirculated exhaust gas produced in this way forms the charge air which is supplied to the compressor and compressed.
Since, within the low-pressure EGR arrangement, exhaust gas is commonly conducted through the compressor, said exhaust gas must be previously subjected to exhaust-gas aftertreatment, in particular in a particle filter. Depositions in the compressor which change the geometry of the compressor, in particular the flow cross sections, and thereby impair the efficiency of the compressor, must be prevented.
For the reasons stated above, embodiments of the internal combustion engine are advantageous in which the recirculation line of the exhaust-gas recirculation arrangement branches off from the exhaust-gas discharge system downstream of the turbine of the at least one exhaust-gas turbocharger and issues into the intake system upstream of the compressor.
In the case of internal combustion engines in which each cylinder has at least two inlet openings, the intake lines of each cylinder of the second group may merge to form a partial intake line, and each partial intake line may be equipped with an inlet-side throttle element. In one embodiment, a single throttle element is sufficient to reduce or stop the supply of charge air to a deactivated cylinder, specifically even if the switchable cylinder has more than one inlet opening, that is to say has at least two inlet openings and thus at least two intake lines.
In the case of internal combustion engines in which the second cylinder group has at least two inlet openings, the intake lines of the second cylinder group may merge to form an overall intake line, thus forming an inlet manifold, and said inlet manifold is equipped with at least one inlet-side throttle element. An inlet-side throttle element may be arranged in the overall intake line of the inlet manifold. A single throttle element may be sufficient to reduce or stop the charge-air supply to the deactivated cylinder group.
In another embodiment, a throttle element may be provided in each intake line of a deactivatable cylinder, though this increases the number of throttle elements required, in particular if the cylinders have more than one inlet opening and/or the second group comprises more than one deactivatable cylinder.
Each outlet valve may be associated with an at least partially variable valve drive which is adjustable with regard to the valve lift Δh. A lifting valve which is adjustable in terms of the valve lift Δh exhibits the normal lift in the case of activated cylinders. Furthermore, a lifting valve of said type permits at least one further actuation with reduced lift. That is to say, a lifting valve which is adjustable in the above sense is a lifting valve which permits at least two different valve lifts Δh1, Δh2. A switchable valve which exhibits zero lift in the deactivated state is thus likewise a valve which is adjustable in terms of valve lift Δh. In one embodiment the outlet valve in question may not be a deactivatable valve.
Each outlet valve may be associated with an at least partially variable valve drive which is adjustable with regard to the opening duration Δt. A lifting valve which is adjustable in the above sense then makes it possible to realize at least two different opening durations Δt1, Δt2. In the case of an activated cylinder group, it is basically the case that a normal opening duration is realized, that is to say an opening duration such as for example the opening duration of the outlet openings of the other first cylinder group. Furthermore, at least one further actuation with a shortened opening duration is possible. A deactivated valve, which is not actuated and thus not opened, has an opening duration of zero. In one embodiment, the outlet valve in question may not be a deactivatable valve. Thereby, each outlet valve may be associated with an at least partially variable valve drive which is adjustable with regard to the valve lift Δh and the opening duration Δt. Each outlet valve associated with an at least partially variable valve drive may be a valve which is adjustable in stepped fashion. As mentioned above, a lifting valve which is adjustable in stepped fashion, in particular two-stepped fashion may be used.
In one example, each outlet valve associated with an at least partially variable valve drive is a continuously adjustable valve. A continuously adjustable outlet valve permits more flexible control of the exhaust-gas flow and/or of the charge-air flow out of a deactivated cylinder.
Each inlet-side throttle element may be arranged as close as possible to the associated cylinder. The smaller the line volume between a throttle element and the associated inlet opening, the more advantageous this is for the operation of the internal combustion engine, especially for the activation and deactivation of the cylinders of the second group.
At least one switchable cylinder of the second group may be switched as a function of the load T of the internal combustion engine, in such a way that at least one switchable cylinder is deactivated if a predefinable load Tdown is undershot and is activated if a predefinable load Tup is exceeded. The charge-air flow rate supplied to the at least one deactivated cylinder during the partial deactivation may be reduced by actuation of the at least one inlet-side throttle element.
The limit loads Tdown and Tup predefined for the undershooting and exceedance respectively may be of equal magnitude, though may also differ in magnitude. When the internal combustion engine is in operation, the cylinders of the first cylinder group are cylinders which are permanently in operation. Switching of the second cylinder group, that is to say an activation and deactivation of said second group, takes place. At least one cylinder of the second group may be deactivated when the predefined load Tdown is undershot and the present load remains lower than said predefined load Tdown for a predefinable time period Δt1.
The introduction of an additional condition for the deactivation of the cylinders of the second group, that is to say the partial deactivation, is intended to prevent excessively frequent activation and deactivation, if the load falls below the predefined load Tdown only briefly and then rises again, or fluctuates around the predefined value for the load Tdown, without the undershooting justifying or necessitating a partial deactivation. Thereby at least one cylinder of the second group is activated when the predefined load Tup is exceeded and the present load remains higher than said predefined load Tup for a predefinable time period Δt2.
Fuel supply to the at least one switchable cylinder may be deactivated in the event of deactivation. This yields advantages with regard to fuel consumption and pollutant emissions, thus assisting the aim pursued by the partial deactivation, specifically that of reducing fuel consumption and improving efficiency. In the case of auto-ignition internal combustion engines, it may even be necessary to deactivate the fuel supply in order to reliably prevent an ignition of the mixture situated in the cylinder.
Upon deactivation of the at least one load-dependently switchable cylinder, the fuel supply of the at least one switchable cylinder may firstly be deactivated before the at least one inlet-side throttle element is actuated. Also, upon activation of the at least one deactivated cylinder, the at least one inlet-side throttle element may firstly be actuated before the fuel supply of the at least one deactivated cylinder is activated.
This approach ensures stable transient operating behavior of the turbocharger of a supercharged internal combustion engine and of the internal combustion engine itself, and makes allowance for the fact that the fuel supply of the internal combustion engine can be deactivated and reactivated directly, that is to say with little time delay, whereas, during the course of the partial deactivation, that is to say upon deactivation of the switchable cylinders and upon reactivation of the deactivated cylinders, the turbocharger responds only with a certain time delay, that is to say reacts in a delayed manner to changes. At least one cylinder which is in operation may be fired by means of auto-ignition. The above method variant relates to methods in which the combustion is initiated by means of auto-ignition, and thus also to operating processes such as are conventionally used in diesel engines.
Each cylinder may be equipped with an ignition device for the initiation of an applied ignition, wherein the ignition device of the at least one switchable cylinder may be preferably deactivated in the event of deactivation. The above method variant relates to the use of the method in the case of an applied-ignition internal combustion engine, for example a direct-injection Otto-cycle engine, the cylinders of which are equipped in each case with an ignition device for initiating an applied ignition.
It is however also possible, for the operation of an Otto-cycle engine, to use a hybrid combustion process with auto-ignition, for example the Homogeneous charge compression ignition (HCCI) method, which is also referred to as the spatial ignition method or as the cold air intake (CAI) method. Said method is based on a controlled auto-ignition of the fuel supplied to the cylinder. Here, the fuel (as in the case of a diesel engine) is burned with an excess of air, that is to say superstoichiometrically. The lean-burn Otto-cycle engine, owing to the low combustion temperatures, has relatively low nitrogen oxide emissions and, likewise owing to the lean mixture, has no soot emissions. Furthermore, the HCCI method leads to high thermal efficiency. Here, the fuel may be introduced both directly into the cylinders and also into the intake pipe.
The predefinable load Tdown and/or Tup may be dependent on the engine speed n of the internal combustion engine. Then, there is not only one specific load, upon the undershooting or exceedance of which switching takes place regardless of the engine speed n. Instead, an engine-speed-dependent approach is followed, and a region in the characteristic map is defined in which partial deactivation takes place. Other operating parameters of the internal combustion engine, for example the engine temperature or the coolant temperature after a cold start of the internal combustion engine may be taken into consideration as a criterion for a partial deactivation.
A predefinable minimum amount of charge air, and no less, may be supplied to the at least one deactivated cylinder. In this respect, a valve arranged in the intake line of a switchable cylinder is not completely closed during the partial deactivation or in the event of a partial deactivation. If a flap is used as a throttle element, it is not a disadvantage that said flap exhibits a leakage flow in the closed position.
The charge-air flow rate supplied to the at least one deactivated cylinder may be co-determined by the load T, the engine speed n, the coolant temperature, the oil temperature, the engine temperature and/or the like.